1. Field of the Invention
The present invention relates to a connecting member between wiring films, a manufacturing method thereof, and a manufacturing method of a multilayer wiring substrate, and specifically, to a connecting member between wiring films, a manufacturing method thereof, and a manufacturing method of a multilayer wiring substrate which are preferably applied to the case where the connecting between wiring films of the multilayer wiring substrate is performed by using a bump made of copper, for example.
2. Description of the Related Art
As one of the methods of performing the connecting between wiring films of a multilayer wiring substrate, there is a method of using a bump made of copper, for example. The method will be simply described with reference to FIG. 26.
A. First, a multilayer metal plate 1 is prepared as shown in FIG. 26(A). The multilayer metal plate 1 is formed by laminating a wiring film forming metal layer 4 that is made of copper foil having a thickness of, for example, 18 μm, through an etching stopping layer 3 that is made of nickel having a thickness of, for example, 1 μm, on one of principal surfaces of a bump forming metal layer 2 that is made of copper foil having a thickness of, for example, 100 μm.
B. The bump forming metal layer 2 of the multilayer metal plate 1 is subjected to selective etching to form bumps 2a for connecting between the wiring films, as shown in FIG. 26(B).
C. When the etching treatment is completed, as shown in FIG. 26(C), an etching treatment with respect to the etching stopping layer 3 is conducted by using copper as a mask, copper being used in forming the bumps 2a and the wiring film forming metal layer 4.
D. An insulating film 5 made of, for example, thermosetting resin is then bonded to the formed surface of the bump 2a so as to expose the top portion of the bump 2a, as shown in FIG. 26(D).
E. Thereafter, a wiring film forming metal thin plate 6 made of, for example, copper is provided so as to face a surface of the multilayer metal plate 1 from which the top portion of the bump 2a is projected, as shown in FIG. 26(E).
F. The wiring film forming metal thin plate 6 is connected to the bump 2a to be laminated on the formed surface side of the bump 2a, as shown in FIG. 26(F).
G. The wiring film forming metal layer 4 of the multilayer metal plate 1 and the wiring film forming metal thin plate 6 are subjected to patterning treatment by selective etching, to thereby form wiring films 4a and 6a. Thus, a multilayer wiring substrate 7 is completed as shown in FIG. 26(G). The wiring films 4a become the wiring films of the upper layer, and the wiring films 6a become the wiring films of the lower layer. When the number of layers is further increased, a wiring substrate in the state shown in FIG. 26(D) is laminated on the multilayer wiring substrate 7, for example.
In the above-described conventional technique, the multilayer metal plate 1 is employed. As described above, the multilayer metal plate 1 has the three-layer structure made of, for example, a copper layer, a nickel layer and a copper layer. The multilayer metal plate 1 is not a general-purpose component such as a simple copper foil but a custom-made component. Therefore, the unit price is expensive.
Also, in the above-described conventional technique, the bumps 2a are formed by first etching, and the removal of the etching stopping layer 3 is performed by second etching. Thus, it is necessary that the different kinds of etching are performed at least twice. Therefore, the number of steps for the processes is increased, and the etching material cost is also increased since different materials are used for selective etching.
In the above-described conventional technique, when the number of the layers is increased, it is necessary to repeat the steps of, for example, forming the wiring films 4a on the wiring film forming metal layer 4 by etching, to laminate the wiring substrate in the state shown in FIG. 26(D) thereon; and forming the next wiring films 4a on the wiring film forming metal layer 4 by etching, to laminate the next wiring substrate in the state shown in FIG. 26(D) thereon. Therefore, it is impossible to stack a desired number of layers at a time to press them collectively.
Also, in the above-described conventional technique, etching resist patterns 8 corresponding to the bumps are formed on the bump forming metal layer 2 and the etching is conducted by using the patterns 8 as the masks, to thereby form the bumps 2a, as shown in FIG. 27. However, in this case, the diameter of each of the etching resist patterns 8 is not allowed to be set to a value equal to or smaller than a given value in relation to the depth of the etching. Also, it is necessary to provide gaps G having the distance equal to or larger than a given value between the etching resist patterns 8. Therefore, the pitch of the etching resist pattern 8, in other words, the pitch of the bump 2a, is not allowed to be set to a value smaller than a given value. For example, when the metal layer has a thickness of 0.1 mm, the pitch has a limitation of 0.4 mmP (Here, foot portion of the bump has a diameter of 0.15 mm.)
In the above-described conventional technique, the wiring film forming metal layer 4 is necessary to have the thickness capable of resisting the conveyance with a conveyor in order to support the bumps 2a to be formed. The metal layer 4 having an extremely thin thickness causes wrinkles, scars, and breaks in the process, and thus, can not be substantially adopted. The step that adopts the semi-additive process that enables minuteness compared with a subtracting process is convenient as long as metal foils with a thickness of about 3 to 5 μm can be used on both sides of the insulating film 5. However, with the above reason, it is difficult to form the wiring layers with a thickness of about 3 to 5 μm.
Also, in the above-described conventional technique, when the bump 2a is heightened, the diameter of a so-called foot portion of the bump 2a is also inevitably increased. Therefore, in the state where the bump 2a is heightened, it is impossible to set a pitch of the bump 2a to a value equal to or smaller than a certain degree.